1. Field of the Invention
The present invention relates to a body frame structure of a straddle-type four wheeled vehicle which is suitable for rough ground travel.
2. Description of the Related Art
The body frame of the straddle-type four wheeled vehicle has been conventionally structured by steel frame members such as a steel pipe or the like, as described in Japanese examined publication, H06-92233, and has been generally structured such that the steel pipes are connected to each other by welding or the like.
As in the conventional example mentioned above, the body frame structured by the steel frame members can sufficiently maintain strength only by welding the steel pipes, and does not require a lot of reinforcing parts. However, this design causes an increase in the weight of a vehicle body and an increase of the material cost.
With respect to the steel body frame mentioned above, in order to reduce weight of the steel body frame, the body frame (an aluminum frame) is made of aluminum or alloy including aluminum. However, it is impossible to sufficiently secure the strength by the structure in which the frame members of the aluminum pipes or the like are simply directly connected to each other by welding. Namely, the strength of the structure consisting of the welded aluminum pipes or the like is less than the strength of the structure consisting of the welded steel pipes or the like. Accordingly, it is necessary to add a lot of reinforcing members to the respective connected portions, the various parts support portions, and the various parts mounting portions, resulting in a lot of trouble during manufacturing and assembling.